Screw caps for containers having a threaded neck portion have been known in the art for a very long time.
Usually, both the screw cap and the neck portion are made of polymer material, comprising one or more complementary threaded portions for screwing the cap onto the neck.
In the food packaging industry, containers and especially packaging containers with a bottle-like shape, having a body portion of a packaging material laminate and a top portion of polymer material including a threaded neck part are well known. Examples of such packaging containers are Tetra Top™, Tetra Evero™ and Tetra Evero Aseptic™ wherein the latter additionally comprises an oxygen barrier in the form of an aluminium foil as part of the packaging material laminate for longer storage time of the foodstuff contained in the packaging container.
After a web of paper material is laminated with several outer polymer materials, folded and spliced to form a hollow packaging container body, a top portion comprising threaded neck part is injection moulded onto the body, which may be of different material than the top portion as evident from the packaging containers mentioned in the previous paragraph. In the next step, a cap application unit screws a threaded cap usually made of polymer material onto threaded neck portion of the packaging container comprising complementary threads. In the ensuing step, the hollow side of the packaging container is filled with the foodstuff to be contained whereafter the hollow end of the container is folded and sealed. It should be mentioned, that in one possible and known implementation of the capping process, the hollow packaging container body including the injection moulded top portion is fed into a rotating drum and rotated to face a screw cap holder while at a distance a screw cap is fed to the screw cap holder. While both the packaging container and the screw cap holder are locked in their radial positions, the screw cap is rotatingly moved towards the top portion of the packaging container and screwed onto its neck portion.
Experience shows that a small percentage of the thus capped package containers display a misalignment between the cap and the neck part of the container. However, the problem exists also for other types of containers, where the top and the body portion are made of the same material, such as a polymer material. Such misalignment has the effect of not sufficiently sealed container, damaged threaded portions on the neck part and the cap itself or too easy opening of the container. Containers with these deviations need to be discarded.
It can be shown that besides reasons mentioned and dealt with in a pending application filed by the applicant, one reason for the misalignment problem lies in the path length the cap has to travel before it hits the start of a thread on the threaded neck portion of the container. Especially in the case when at least one of the threads in the cap may hit the start of either one of two threads on the threaded part of the container neck, obliquely applied or tilted caps are likely to occur.